The present invention relates to a crystal growing apparatus for growing crystals by the Czochralski method or by the ribbon pulling method.
The Czochralski method or ribbon pulling method is widely applied to the production of a crystal ingot of silicon or the like. In a crystal growing apparatus adopting the Czochralski method, polysilicon and a dopant (impurity) as raw materials are charged in a quartz crucible. The crucible is heated to hold a melt of the raw materials therein. A seed crystal attached at the lower end of a pulling shaft is brought into contact with the melt held in the crucible while the pulling shaft is gradually pulled upward. Thus, a crystal is grown on the lower end of the seed crystal. Meanwhile, in a crystal growing apparatus adopting the ribbon pulling method, the sectional shape of a melt is regulated to be rectangular so as to prepare a ribbon-shaped crystal.
However, in the conventional apparatus as described above, as the crystal grows, the amount of the melt in the crucible linearly decreases. For this reason, it has been difficult to produce a crystal ingot having a constant diameter or a ribbon-shaped crystal having a constant width and thickness. Furthermore, since polysilicon can only be supplied to the crucible in the charging step prior to pulling, the raw materials for only one pulling step can be charged in the crucible. This requires charging of polysilicon for each pulling step, which is uneconomic.
In order to solve these problems, it has been proposed to incorporate a raw material replenishment means in a crystal pulling mechanism. However, the techniques of such replenishment of raw materials do not resolve the problems of either short supply of raw materials in the crucible or of overflow of raw materials from the crucible. This proposal therefore has not actually been adopted.